Many electrical components used in electric circuits suffer from parametric variation as a result of changes in ambient temperature. These parameters include resistance, inductance and capacitance in passive circuits, and gain, distortion, and noise in active circuits. In both active and passive devices parametric changes can produce changes in phase. For example, considering the low pass filter 10 shown in FIG. 1 which comprises a resistor 12 and capacitor 14 connected in series along a line between ports 16 and 18. The phase shift from port 16 to port 18 will change as the value of the resistor 12 varies with temperature. If the resistance of the resistor 12 is 2 ohms, the phase at 1500 Mhz is -2.7.degree., while if the resistance is 50 ohms the phase is -10.degree.. The phase shift will similarly change as the capacitance of the capacitor 14 varies with temperature.
Another common circuit element that suffers from phase variation with temperature is the delay line. Delay lines are used to produce signal propagation delays in radar and communication systems. Delay lines are often produced by coiling coaxial transmission lines. A typical coaxial line will have a phase variation of about -100 ppm/.degree. C. If many such components are used in a complicated device, such as a multistage amplifier or filter, the resulting phase variation with temperature can be large.
Many active devices are available to compensate for phase variations including digital step phase shifters, and analog phase shifters. The step type phase shifter switches in or out discrete phase shifts such that the sum equals the desired total shift. The analog type phase shifter creates four mutually orthogonal vectors and then varies the magnitude of each to form a single recombined vector at the desired phase. However, in each of these types of phase shifters additional temperature sensors and drives would be required to use these devices for temperature compensation. Active devices have the additional problems of size, complexity, reliability, DC power consumption, cost and the introduction of distortion and switching transients as a result of the nonlinear control devices.